Extruded polystyrene foam and method for producing same

ABSTRACT

An extruded polystyrene foam which is obtained by performing extrusion foaming using a styrene resin and a foaming agent, contains a flame retardant in a proportion of 0.5 parts by weight or more and 8.0 parts by weight or less based on 100 parts by weight of the styrene resin and has an apparent density of 20 kg/m 3  or more and 45 kg/m 3  or less and a closed cell ratio of 90% or more, in which the foaming agent at least contains HFO and another organic foaming agent,
         (i) the blended amount of the HFO is 0.030 mol or more and 0.125 mol or less based on 100 g of the styrene resin,   (ii) an organic foaming agent having a polystyrene permeability of 0.5×10 −10  cc·cm/cm 2 ·s·cmHg or more is contained as the another organic foaming agent,   (iii) an organic foaming agent having a polystyrene permeability of less than 0.5×10 −10  cc·cm/cm 2 ·s·cmHg is not contained as the another organic foaming agent, and   (iv) the total blended amount of the HFO and the another organic foaming agent is 0.105 mol or more and 0.300 mol or less based on 100 g of the styrene resin.

TECHNICAL FIELD

The present invention relates to an extruded polystyrene foam and amethod for producing the same.

BACKGROUND ART

The extruded polystyrene foam is continuously produced by heating andmelting a styrene resin composition using an extruder or the like,adding a foaming agent under high-pressure conditions, cooling theresultant mixture to a predetermined resin temperature, and thenextruding the resultant mixture into a low-pressure area.

The extruded polystyrene foam is used as, for example, heat insulatingmaterials for structures due to good workability and insulationproperties. In recent years, a demand for energy saving of residences,buildings, and the like has increased, so that a technical developmentof a higher heat insulating foam than before has been desired.

Heretofore, chlorofluorocarbon (hereinafter referred to as CFC), such asdichlorodifluoromethane, has been widely used as a physical foamingagent for use in production of the extruded polystyrene foam. However,CFC has a high risk of destroying the ozone layer, and therefore ahydrogen atom containing chlorofluorocarbon (hereinafter referred to asHCFC) with a small ozone depletion potential has been used as asubstituent for the CFC. However, the ozone depletion potential of theHCFC is also not 0 (zero), and therefore it cannot be said that the HCFCis completely free from a risk of destroying the ozone layer. Thus, inrecent years, hydrofluorocarbon (hereinafter referred to as HFC) whichhas an ozone depletion potential of 0 (zero) and does not have achlorine atom in the molecules has been increasingly used as the foamingagent.

For example, Patent Document 1 discloses, as a method for producing apolystyrene resin foam which has excellent heat insulation performanceover a long period of time and which can be suitably used for heatinsulating materials for houses and the like using a fron-based foamingagent having an ozone depletion potential of 0, a method for producing afoam having a density of 2×10⁻² to 4.5×10⁻² g/cm³ including pressing afoaming agent obtained by mixing trifluoroethane which is one kind ofHFC and methyl chloride into a polystyrene resin for extrusion foaming.However, there has been a problem that the HFC has a high global warmingpotential.

Thus, a method for producing an extruded polystyrene foam insulatingboard using a fluorinated olefin (hydrofluoroolefin, which is alsoreferred to as HFO) which has an ozone depletion potential of 0 (zero)and has a small global warming potential, and thus is friendly to theenvironment as an alternative foaming agent of the HFC has been proposed(for example, refer to Patent Documents 2 to 5). However, these formertechniques have not succeeded in obtaining an extruded polystyrene foamhaving excellent heat insulation properties and flame retardancysufficiently utilizing the merits (low thermal conductivity, flameretardancy) of using the hydrofluoroolefin, and thus these formertechniques still have had problems.

CITATION LIST Patent Literatures

Patent Document 1: JP-A No. H08-269224

Patent Document 2: JP-A No. 2012-007094

Patent Document 3: JP-T No. 2008-546892

Patent Document 4: JP-A No. 2013-194101

Patent Document 5: JP-T No. 2010-522808

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to easily obtain an extrudedpolystyrene foam, which is lightweight and has excellent heat insulationproperties and flame retardancy, has an ozone depletion potential of 0,and has a small global warming potential, and thus is friendly to theenvironment.

Solution to Problem

The present inventors have conducted an extensive research in order tosolve the above-described problems, and, as a result, accomplished thepresent invention by the use of a specific amount of a mixed foamingagent of HFO and a specific organic foaming agent as a physical foamingagent for the production of an extruded polystyrene foam.

More specifically, the present invention is as follows.

[1] An extruded polystyrene foam which is obtained by performingextrusion foaming using a styrene resin and a foaming agent, contains aflame retardant in a proportion of 0.5 parts by weight or more and 8.0parts by weight or less based on 100 parts by weight of the styreneresin, and has an apparent density of 20 kg/m³ or more and 45 kg/m³ orless and a closed cell ratio of 90% or more, in which the foaming agentat least contains hydrofluoroolefin and another organic foaming agent,

(i) the blended amount of the hydrofluoroolefin is 0.030 mol or more and0.125 mol or less based on 100 g of the styrene resin,

(ii) an organic foaming agent having a polystyrene permeability of0.5×10⁻¹⁰ cc·cm/cm²·s·cmHg or more is contained as the another organicfoaming agent,

(iii) an organic foaming agent having a polystyrene permeability of lessthan 0.5×10⁻¹° cc·cm/cm²·s·cmHg is not contained as the another organicfoaming agent, and

(iv) the total blended amount of the hydrofluoroolefin and the anotherorganic foaming agent is 0.105 mol or more and 0.300 mol or less basedon 100 g of the styrene resin.

[2] The extruded polystyrene foam according to [1], in which the blendedamount of the hydrofluoroolefin is 0.040 mol or more and 0.105 mol orless based on 100 g of the styrene resin.[3] The extruded polystyrene foam according to [1] or [2], in which thehydrofluoroolefin is tetrafluoropropene.[4] The extruded polystyrene foam according to any one of [1] to [3], inwhich the another organic foaming agent is one kind or a mixturecontaining two or more kinds selected from dimethylether, methylchloride, and ethyl chloride.[5] The extruded polystyrene foam according to any one of [1] to [4], inwhich the another organic foaming agent is dimethylether.[6] The extruded polystyrene foam according to any one of [1] to [5],containing, as the flame retardant, a bromine-based flame retardant in aproportion of 0.5 parts by weight or more and 6.0 parts by weight orless based on 100 parts by weight of the styrene resin.[7] A method for producing an extruded polystyrene foam by performingextrusion foaming using a styrene resin and a foaming agent, and themethod includes heating and melting a styrene resin compositioncontaining a flame retardant in a proportion of 0.5 parts by weight ormore and 8.0 parts by weight or less based on 100 parts by weight of thestyrene resin, adding the foaming agent under high-pressure conditions,cooling the resultant mixture to a predetermined resin temperature, andthen extruding the cooled mixture into a low-pressure area to mold anextruded foam having an apparent density of 20 kg/m³ or more and 45kg/m³ or less and a closed cell ratio of 90% or more, in which

at least hydrofluoroolefin and another organic foaming agent are used asthe foaming agent,

(i) the blended amount of the hydrofluoroolefin is 0.030 mol or more and0.125 mol or less based on 100 g of the styrene resin,

(ii) an organic foaming agent having a polystyrene permeability of0.5×10⁻¹⁰ cc·cm/cm²·s·cmHg or more is used as the another organicfoaming agent,

(iii) an organic foaming agent having a polystyrene permeability of lessthan 0.5×10¹⁰ cc·cm/cm²·s·cmHg is not used as the another organicfoaming agent, and

(iv) the total blended amount of the hydrofluoroolefin and the anotherorganic foaming agent is 0.105 mol or more and 0.300 mol or less basedon 100 g of the styrene resin.

Advantageous Effects of Invention

According to the present invention, an extruded polystyrene foam whichis lightweight and has excellent heat insulation properties and flameretardancy, has an ozone depletion potential of 0, and has a smallglobal warming potential, and thus is friendly to the environment can beeasily obtained.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention is described. Thisembodiment is merely a part of the present invention, and thus it is amatter of course that this embodiment can be altered as appropriateinsofar as the scope of the present invention is not altered.

An extruded polystyrene foam of the present invention contains a flameretardant in a proportion of 0.5 parts by weight or more and 8.0 partsby weight or less based on 100 parts by weight of a styrene resin, inwhich the apparent density is 20 kg/m³ or more and 45 kg/m³ or less andthe closed cell ratio is 90% or more. The extruded polystyrene foam iscontinuously produced by heating and melting a styrene resin compositioncontaining a specific amount of a flame retardant and, as necessary, aproper amount of other additives using an extruder or the like, adding aspecific amount of a specific mixed foaming agent containing HFO underhigh-pressure conditions, cooling the resultant mixture to apredetermined resin temperature, and then extruding the cooled mixtureinto a low-pressure area.

The styrene resin for use in the present invention is not particularlylimited and examples of the styrene resin include homopolymers ofstyrene monomers such as styrene, methylstyrene, ethylstyrene,isopropylstyrene, dim ethylstyrene, bromostyrene, chlorostyrene,vinyltoluene, and vinylxylene, or copolymers of two or more of themonomers, copolymers obtained by copolymerization of the styrene monomerwith at least one or two or more of monomers such as divinylbenzene,butadiene, acrylic acid, methacrylic acid, methyl acrylate, methylmethacrylate, acrylonitrile, maleic anhydride, and itaconic anhydride,and the like. The monomers to be copolymerized with the styrene monomer,such as acrylic acid, methacrylic acid, methyl acrylate, methylmethacrylate, maleic anhydride, and itaconic anhydride, can be used withsuch an amount that the physical properties, such as compressivestrength, of the extruded polystyrene foam to be produced are notimpaired. The styrene resin for use in the present invention is notlimited to the homopolymers or the copolymers of the styrene monomersand may be a blend of the homopolymers or the copolymers of the styrenemonomers and the homopolymers or the copolymers of the other monomers,and a diene rubber reinforced polystyrene or an acrylic rubberreinforced polystyrene can be blended. The styrene resin for use in thepresent invention may be a styrene resin having a branched structure forthe purpose of adjusting the melt flow rate (hereinafter also referredto as MFR), a melt viscosity and a melt tension in molding, and thelike.

As the styrene resin in the present invention, a styrene resin having anMFR of 0.1 to 50 g/10 minutes is preferably used in the respect that athermoplastic resin foam in which the moldability in extrusion foammolding is excellent, the discharge amount in molding, the thickness andthe width and the apparent density or the closed cell ratio of theobtained extruded polystyrene foam are easily adjusted to desiredvalues, and the foamability (the foamability becomes better when thethickness and the width, the apparent density, the closed cell ratio,the surface properties, and the like of a foam are more easilyadjusted), the appearance, and the like are good can be obtained, and anextruded polystyrene foam having well-balanced characteristics such asmechanical strengths including compressive strength, bending strength,and bending deflection and toughness can be obtained. The MFR of thestyrene resin is preferably 0.3 to 30 g/10 minutes and more preferably0.5 to 25 g/10 minutes in the respect that the balance between themechanical strength, toughness, and the like and the moldability and thefoamability. In the present invention, the MFR is measured by the methodA in the test condition H of JIS K7210 (1999).

In the present invention, among the styrene resin mentioned above,polystyrene resin is suitable in the respect of economical efficiencyand processability. When higher heat resistance is required in anextruded foam, it is preferable to use a styrene-acrylonitrilecopolymer, (meth)acrylic acid-copolymerized polystyrene, maleicanhydride-modified polystyrene. When a higher impact resistance isdemanded in an extruded foam, it is preferable to use rubber-reinforcedpolystyrene. The styrene resin may be used alone or two or more kinds ofstyrene resin different in a copolymerization component, a molecularweight and a molecular weight distribution, a branched structure, anMFR, and the like may be used as a mixture.

In the present invention, a mixed foaming agent of hydrofluoroolefin anda specific organic foaming agent is used as the foaming agent.

Examples of the hydrofluoroolefins include, for example,tetrafluoropropene, and specifically, trans-1,3,3,3-tetrafluoropropene(trans-HFO-1234ze), cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze),2,3,3,3-tetrafluoropropene (HFO-1234yf), and the like. Thesehydrofluoroolefins may be used alone or in combination of two or morekinds thereof.

The hydrofluoroolefin has an ozone depletion potential of 0 or a verysmall ozone depletion potential and has a very small global warmingpotential, and thus is an environmentally friendly foaming agent.Moreover, the hydrofluoroolefin has a low thermal conductivity in a gasstate and is fire retardant, and therefore, the hydrofluoroolefin cangive excellent heat insulation properties and flame retardancy by theuse of the hydrofluoroolefin as the foaming agent of an extrudedpolystyrene foam.

Heretofore, HFO having relatively high solubility in polystyrene resinand having high compatibility with polystyrene resin, i.e., HFO whicheasily dissipates from the inside of a foam but a large amount of whichcan be added to polystyrene resin and which is excellent in foamingcapability among HFOs, has been preferably used as the foaming agent,and an extruded foam with high foaming ratio has been able to beobtained.

On the other hand, in the case where tetrafluoropropene (1234ze, 1234yf)and the like which are HFOs having low solubility in polystyrene resinand low compatibility with polystyrene resin are used as the foamingagent, when a large amount of the tetrafluoropropene is added in orderto obtain a foam having a high foaming ratio, the tetrafluoropropenedissociates from a resin melted substance in extrusion foaming, so thata largely recessed portion (hereinafter sometimes also referred to as aspot hole) is locally formed in the surface of the foam, which raises apossibility that the appearance of an insulating board deteriorates.When producing a foam having a large thickness, there has been apossibility that the closed cell ratio decreases and the long-term heatinsulation properties decrease.

In the present invention, however, even in the case where HFO havingrelatively low solubility in polystyrene resin is used, the use of aspecific mixed physical foaming agent allows the formation of a foamhaving a high foaming ratio and further allows the formation of apolystyrene resin foam having excellent long-term heat insulationproperties and good appearance.

In the mixed foaming agent of the present invention, the blended amountof the hydrofluoroolefin is 0.030 mol or more and 0.125 mol or lessbased on 100 g of the styrene resin. When the blended amount of thehydrofluoroolefin is less than 0.030 mol based on 100 g of the styreneresin, an improvement effect of the heat insulation properties due tothe hydrofluoroolefin cannot be expected. On the other hand, when theblended amount of the hydrofluoroolefin exceeds 0.125 mol based on 100 gof the styrene resin, the hydrofluoroolefin dissociates from a resinmelted substance in extrusion foaming, which raises a possibility that aspot hole is formed in the surface of a foam or the closed cell ratiodecreases. The blended amount of the hydrofluoroolefin is preferably0.035 mol or more and 0.115 mol or less, more preferably 0.040 mol ormore and 0.105 mol or less, and still more preferably 0.045 mol or moreand 0.090 mol or less based on 100 g of the styrene resin.

Examples of the organic foaming agent include saturated hydrocarbonshaving 3 to 5 carbon atoms such as propane, normal butane,isobutane(2-methyl propane), and cyclopentane, ethers such asdimethylether, ethyl ether, diethylether, and methyl ethyl ether, alkylchlorides such as methyl chloride and ethyl chloride, alcohols such asmethanol, ethanol, propyl alcohol, isopropyl alcohol, butyl alcohol,sec-butyl alcohol, tert-butyl alcohol, aryl alcohol, crotyl alcohol, andpropargyl alcohol, ketones, esters, and the like. Among the above,another organic foaming agent to be used in combination with thehydrofluoroolefin in the present invention is required to have apolystyrene permeability of 0.5×10⁻¹⁰ cc·cm/cm²·s·cm·Hg or more.Furthermore, the polystyrene permeability is more preferably 1.0×10⁻¹⁰cc·cm/cm²·s·cm·Hg or more.

The organic foaming agents mentioned above have a high plasticizationeffect of the styrene resin and are required in order to foam a styreneresin melted substance containing a styrene resin, a foaming agent, aflame retardant, and other various additives with a proper viscosity toobtain a desired extruded foam. On the other hand, the flame retardancyis adversely affected, and therefore, by selecting an organic foamingagent which has a high polystyrene permeability and promptly dissipatesafter forming an extruded foam, excellent processability and foamabilityare obtained when producing an extruded foam and also excellent flameretardancy can be given to an extruded foam.

Other organic foaming agents to be used in combination with thehydrofluoroolefin in the present invention are not particularly limitedinsofar as the polystyrene permeability is 0.5×10⁻¹⁰ cc·cm/cm²·s·cm·Hgor more and are preferably ethers and alkyl chlorides because theplasticization effect of the styrene resin is high and the polystyrenepermeability is high. Among the above, dimethylether, methyl chloride,and ethyl chloride are more preferable, and, in particular,dimethylether is particularly preferable because the polystyrenepermeability is high and a load to the environment is low. These organicfoaming agents can be used alone or as a mixture of two or more kindsthereof.

The polystyrene permeability of the foaming agent in the presentinvention is determined by JIS K 7126A method. For example, thepolystyrene permeability can be measured by fixing a polystyrene resinfilm having a thickness of 50 to 100 μm produced by heating andmelt-pressing a polystyrene resin (manufactured by PS Japan Corporation,Product Name “G9401”) to a differential pressure type gas permeationdevice (manufactured by GTR Tec Corporation, GTR-31A) having a gaschromatograph (manufactured by Yanaco Analytical Systems Inc., G2700T),and then measuring the penetration amount by a differential pressuremethod under the conditions of a temperature of 23° C.±2° C. and a drycondition. An example of the polystyrene permeability of the foamingagent measured as described above is shown in Table 1.

TABLE 1 Organic foaming Polystyrene permeability × agent 10⁻¹⁰ cc ·cm/cm² · s · cmHg Propane 0.030 Normal butane 0.015 Isobutane 0.005Dimethylether 3.30 Methyl chloride 7.26 Ethyl chloride 1.00

The total blended amount of the hydrofluoroolefin and the other organicfoaming agents is preferably 0.105 mol or more and 0.300 mol or lessbased on 100 g of the styrene resin and more preferably 0.115 mol ormore and 0.200 mol or less based on 100 g of the styrene resin. When thetotal blended amount of the mixed foaming agent is less than 0.105 molbased on 100 g of the styrene resin, a styrene resin melted substancecontaining a styrene resin, a foaming agent, a flame retardant, othervarious additives, and the like is not imparted with a proper viscosityfor obtaining a desired extruded foam in foaming, and only an extrudedfoam in which the closed cell ratio is less than 90% and/or the apparentdensity is high is obtained. When the total blended amount of the mixedfoaming agent is larger than 0.300 mol based on 100 g of the styreneresin, defects, such as a void, may arise in a foam because the foamingagent is excessively contained.

Moreover, in the present invention, inorganic foaming agents, such ascarbon dioxide and water, can be used as necessary in combination withthe hydroolefin and the other organic foaming agents mentioned above.The inorganic foaming agents can be used alone or as a mixture of two ormore kinds thereof. By the use of the inorganic foaming agents, a goodplasticization effect and a good foaming assistant effect are obtainedand the extrusion pressure is reduced, so that stable production of anextruded foam is achieved.

In the present invention, when water or alcohols is/are used as theother foaming agents, a water-absorbing substance is preferably used forstably performing extrusion foam molding. Specific examples of thewater-absorbing substance for use in the present invention include waterabsorbing polymers such as polyacrylate polymers, starch-acrylic acidgraft copolymers, polyvinyl alcohol polymers, vinyl alcohol-acrylatecopolymers, ethylene-vinyl alcohol copolymers, acrylonitrile-methylmethacrylate-butadiene copolymers, polyethylene oxide copolymers, andderivatives thereof, and fine particles having a hydroxy group on thesurface and having a particle size of 1,000 nm or less such as anhydroussilica (silicon dioxide) having a silanol group on the surface [forexample, “AEROSIL” manufactured by Nippon Aerosil Co., Ltd. iscommercially available]; water absorbable or water swellable layeredsilicates such as smectite and swellable fluorine mica, and organizedproducts thereof; and porous substances such as zeolite, activatedcarbon, alumina, silica gel, porous glass, activated clay, diatomaceousearth, and bentonite. The addition amount of the water-absorbingsubstance is adjusted as appropriate depending on the addition amount ofwater and the like and is preferably 0.01 to 5 parts by weight and morepreferably 0.1 to 3 parts by weight based on 100 parts by weight of thestyrene resin.

The pressure in adding or injecting the foaming agent is notparticularly limited and may be pressure higher than the internalpressure of an extruder or the like.

In the present invention, flame retardancy can be given to an extrudedpolystyrene foam to be obtained by blending a flame retardant in aproportion of 0.5 parts by weight or more and 8.0 parts by weight orless based on 100 parts by weight of the styrene resin. When the contentof the flame retardant is less than 0.5 parts by weight, goodcharacteristics as foams, such as flame retardancy, tend to be hard toobtain. On the other hand, when the content exceeds 8.0 parts by weight,the stability in producing foams, the surface properties, and the likeare impaired in some cases. However, it is preferable to adjust thecontent of the flame retardant as appropriate in such a manner as toobtain the flame retardancy prescribed in JIS A9511, Measurement MethodA according to the content of the foaming agent, the apparent density ofa foam, and the type or the content of additives having a flameretardancy synergistic effect.

As the flame retardant, bromine-based flame retardants are preferablyused. Specific examples of the bromine-based flame retardants in thepresent invention include hexabromocyclododecane, tetrabromobisphenolA-bis(2,3-dibromo-2-methylpropyl)ether, tetrabromobisphenolA-bis(2,3-dibromopropyl)ether, and tris(2,3-dibromopropyl)isocyanurate,and aliphatic bromine containing polymers such as a brominated styrenebutadiene block copolymer. These substances may be used alone or as amixture of two or more kinds thereof.

Among the above, a mixed bromine-based flame retardant containingtetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether andtetrabromobisphenol A-bis(2,3-dibromopropyl)ether,hexabromocyclododecane, and a brominated styrene-butadiene blockcopolymer are preferably used because a good extrusion operation isachieved and the heat resistance of a foam is not adversely affected,for example. These substances may be used alone or as a mixture.

The content of the bromine-based flame retardant in the presentinvention is preferably 0.5 parts by weight or more and 6.0 parts byweight or less based on 100 parts by weight of the styrene resin, morepreferably 1.0 part by weight or more and 5.0 parts by weight or lessbased on 100 parts by weight of the styrene resin, and still morepreferably 1.5 parts by weight or more and 5.0 parts by weight or less.When the content of the bromine-based flame retardant is less than 0.5parts by weight, good characteristics as foams, such as flameretardancy, tend to be hard to obtain. On the other hand, when thecontent exceeds 6.0 parts by weight, the stability in producing foams,the surface properties, and the like may be imp aired.

In the present invention, a radical generating agent can be used incombination for the purpose of increasing the flame retardancyperformance of an extruded polystyrene foam. Specific examples of theradical generating agent include 2,3-dimethyl-2,3-diphenylbutane,poly-1,4-diisopropyl benzene, 2,3-diethyl-2,3-diphenyl butane,3,4-dimethyl-3,4-diphenylhexane, 3,4-diethyl-3,4-diphenylhexane,2,4-diphenyl-4-methyl-1-pentene, 2,4-diphenyl-4-ethyl-1-pentene, and thelike. Peroxides, such as dicumyl peroxide, are also used. Among theabove, those which are stable under a resin treatment temperaturecondition are preferable and specifically 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropyl benzene are preferable. The additionamount is preferably 0.05 to 0.5 parts by weight based on 100 parts byweight of the styrene resin.

Furthermore, for the purpose of increasing the flame retardancyperformance, phosphorus-based flame retardants, such as phosphate esterand phosphine oxide, can be used in combination insofar as the heatstability is not impaired. Examples of the phosphate ester includetriphenyl phosphate, tricresyl phosphate, trixylenylphosphate, cresyldiphenylphosphate, 2-ethylhexyl diphenylphosphate, trimethyl phosphate,triethyl phosphate, tributyl phosphate, tris(2-ethylhexyl)phosphate,tris(butoxyethyl)phosphate, condensed phosphate ester, or the like, andtriphenylphosphate and tris(tributylbromoneopentyl)phosphate areparticularly preferable. As a phosphine oxide type phosphorus-basedflame retardant, triphenylphosphine oxide is preferable. These phosphateesters and phosphine oxides may be used alone or in combination of twoor more kinds thereof. The addition amount of the phosphorus-based flameretardant is preferably 0.1 to 2 parts by weight based on 100 parts byweight of the styrene resin.

In the present invention, resin and/or a stabilizer of a flame retardantcan be used as necessary. Although not particularly limited, specificexamples of the stabilizer include epoxy compounds such as a bisphenol Adiglycidyl ether type epoxy resin, a cresol novolac type epoxy resin,and a phenol novolac type epoxy resin; polyhydric alcohol esters whichare partial esters as reaction products of polyhydric alcohols such aspentaerythritol, dipentaerythritol, and tripentaerythritol, andmonovalent carboxylic acids such as acetic acid and propionic acid, ordivalent carboxylic acids such as adipic acid and glutamic acid, andwhich are mixtures of compounds having one or more hydroxyl groups inthe molecules and contain a small amount of polyhydric alcohols as theraw materials in some cases; phenol stabilizers such astriethyleneglycolbis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, pentaerythritoltetrakis[3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate],octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, andpentaerythritoltetrakis[3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate; phosphitestabilizers such as3,9-bis(2,4-di-tert-butylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane,3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane,and tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4′-biphenylenediphosphonite, are suitably used in terms of not reducing the flameretardancy performance of a foam and increasing the heat stability of afoam.

“Apparent Density”

In the extruded polystyrene foam according to the present invention, theapparent density of the extruded foam is preferably 20 kg/m³ or more and45 kg/m³ or less and more preferably 25 kg/m³ or more and 40 kg/m³ orless from the viewpoint of, for example, the heat insulation propertiesand lightweight properties considering that the extruded polystyrenefoam functions as heat insulating materials for construction or heatinsulating materials for cooling boxes or refrigerating vehicles.

“Closed Cell Ratio”

The closed cell ratio of the extruded polystyrene foam of the presentinvention is preferably 90% or more and more preferably 95% or more.When the closed cell ratio is excessively low, there is a possibilitythat the hydrofluoroolefin used as a foaming agent easily dissipatesfrom the extruded foam at the early stage, so that the long-term heatinsulation properties decrease. In the present invention, the closedcell ratio (%) of the extruded foam is measured using an air comparisontype pycnometer (for example, manufactured by Tokyo Science, Aircomparison type pycnometer, Model: 1000 type) according to Procedure Cof ASTM-D 2856-70.

With respect to the closed cell ratio of the extruded foam in thepresent invention, samples obtained by cutting the extruded foam into asize of 25 mm in length×25 mm in width×20 mm in thickness from threeplaces in total in the vicinity of the central portion and both ends inthe width direction of the extruded foam are used as test samples, eachtest sample is measured for the closed cell ratio by the followingexpression (1), and then the arithmetic mean value of the closed cellratios of the three places is defined as the closed cell ratio of theextruded foam.

Closed cell ratio (%)=(Vx−W/ρ)×100/(VA−W/ρ)  (1)

Vx: True volume of the sample measured by the air comparison typepycnometer (cm³; Total of the capacity of resin configuring the sampleof the extruded foam and the total capacity of all the cells of theclosed cell portion in the sample.)VA: Apparent volume of the sample calculated from the outside dimensionof the sample (cm³)W: Total weight (g) of the sampleρ: Density (g/cm³) of the styrene resin configuring the extruded foam

“Average Cell Diameter”

The average cell diameter (D_(T)) in the thickness direction of theextruded polystyrene foam of the present invention is preferably 0.5 mmor less and more preferably 0.05 to 0.3 mm from the viewpoint of heatinsulation properties.

With respect to the average cell diameter (D_(T): mm) in the thicknessdirection, straight lines over the total thickness of the extruded foamare drawn in the thickness direction on microscope magnified photographsof three portion in total of the central portion and both ends of avertical cross section in the width direction, the average cell diameter(Length of the straight line/Number of the cells crossing the straightline) of the cells present on each straight line is determined from thelength of each straight line and the number of cells crossing thestraight lines, and then the arithmetic mean value of the determinedaverage diameter of the three places is defined as the average celldiameter (D_(T): mm) in the thickness direction.

With respect to the average cell diameter (D_(W): mm) in the widthdirection, straight lines having a length obtained by multiplying 3 mmby the magnification are drawn in the width direction at the positionwhere the extruded foam are bisected in the thickness direction onmicroscope magnified photographs of three portions in total of thecentral portion and both ends of a vertical cross section in the widthdirection, the average diameter of the cells present on each straightline is determined from the straight lines and the number of the cellscrossing the straight lines by Expression [3 mm/(Number of the cellscrossing the straight line−1)], and then the arithmetic mean value ofthe determined average diameter of the three places is defined as theaverage cell diameter (D_(W): mm) in the width direction.

With respect to the average cell diameter (D_(L): mm) in the extrusiondirection, straight lines having a length obtained by multiplying 3 mmby the magnification are drawn in the extrusion direction at theposition where the extruded foam is bisected in the thickness directionon microscope magnified photographs of three portions at an interval of1 m of a vertical cross section in the extrusion direction obtained bycutting the extruded foam in the extrusion direction at a position wherethe width direction of the extruded foam is bisected, the averagediameter of the cells present on each straight line is determined fromthe straight lines and the number of the cells crossing the straightlines by Expression [3 mm/(Number of the cells crossing the straightline−1)], and then the arithmetic mean value of the determined averagediameter of the three places is defined as the average cell diameter(D_(L): mm) in the extrusion direction. The average cell diameter(D_(H): mm) in the horizontal direction of the extruded foam is anarithmetical mean value of D_(W) and D_(L).

“Cell Deformation Ratio”

In the extruded polystyrene foam of the present invention, the celldeformation ratio is preferably 0.7 to 2.0. The cell deformation ratiois a value (D_(T)/D_(H)) obtained by dividing the average cell diameter(D_(T): mm) in the thickness direction determined by the above-describedmeasurement method by the average cell diameter (D_(H): mm) in thehorizontal direction of the extruded foam. When the cell deformationratio is smaller than 1, the cells are more flat. When the celldeformation ratio is larger than 1, the cells are vertically longer.When the cell deformation ratio is excessively small, the cells areflat, so that the compressive strength tends to decrease and the flatcells have a strong tendency of returning to a spherical shape, andtherefore the dimensional stability of the extruded foam also tends todecrease. When the cell deformation ratio is excessively large, thenumber of cells in the thickness direction decreases, so that an effectof improving the heat insulation properties by the cell shape islowered. Therefore, the cell deformation ratio is more preferably 0.8 to1.5 and still more preferably 0.8 to 1.2. When the cell deformationratio is within the ranges mentioned above, an extruded polystyrene foamhaving excellent mechanical strength and high heat insulation propertiesis obtained.

“Thermal Conductivity”

The thermal conductivity (A) after the passage of 100 days after theproduction of the extruded polystyrene foam of the present invention isdesirably 0.0290 W/(m·K) or less and more preferably 0.0280 W/(m·K) orless. The extruded polystyrene foam of the present invention has a highclosed cell ratio and is effectively prevented from dissipation ofhydrofluoroolefin from the foam. Therefore, even after the passage of100 days after the production, the thermal conductivity is maintainedlow and the heat insulation properties are excellent.

In the present invention, the thermal conductivity is measured by amethod according to an accelerating test described in ISO 11561. A testpiece not having a molded skin of 10 mm in thickness×200 mm inlength×200 mm in width is cut out from the central portion in thethickness direction and in the width direction of the extruded foamimmediately after the production, and then the test piece is allowed tostand still under the standard temperature condition, Third class (23°C.±5° C.) and the standard humidity condition, Third class (50⁺²⁰, ⁻¹⁰%R.H.) prescribed in JIS K 7100. After the passage of 100 days after theproduction, the thermal conductivity is measured using the test pieceunder a temperature condition of an average temperature of 23° C. by amethod according to JIS A 1412-2:1999.

As described above, in order to adjust the thermal conductivity afterthe passage of 100 days after the production of the extruded polystyrenefoam to 0.0280 W/(m·K) or less, the blended amount of thehydrofluoroolefin and the apparent density, the closed cell ratio, theaverage cell diameter, and the cell deformation ratio of the extrudedfoam may be adjusted within the ranges specified in the presentinvention.

In the present invention, graphite may be added as a heat ray radiationsuppressor for improving insulation properties. The heat ray radiationsuppressor refers to a substance having a property of reflecting,scattering, and absorbing light in the near infrared region or theinfrared region (for example, wavelength band of about 800 to 3000 nm).By adding the heat ray radiation suppressor, a foam having high heatinsulation properties is obtained. As the heat ray radiation suppressorusable in the present invention, white particles such as titanium oxide,barium sulfate, zinc oxide, aluminum oxide, and antimony oxide can beused in combination besides graphite. These substances may be used aloneor in combination of two or more kinds thereof. Among the above, fromthe respect that the ray radiation control effect is high, titaniumoxide and barium sulfate are preferable and titanium oxide is morepreferable.

The content of the heat ray radiation suppressor in the presentinvention is preferably 1.0 part by weight or more and 6.0 parts byweight or less and more preferably 2.0 parts by weight or more and 5.0parts by weight or less based on 100 parts by weight of the styreneresin. When the content of the heat ray radiation suppressor is lessthan 1.0 part by weight, an improvement of insulation properties is hardto achieve. On the other hand, when the content of the heat rayradiation suppressor exceeds 6.0 parts by weight, the extrusionstability and the moldability tend to be poor or the flammability tendsto be impaired.

In the present invention, the styrene resin may further containadditives, for example, inorganic compounds such as silica, calciumsilicate, wollastonite, kaolin, clay, mica, zinc oxide, titanium oxide,and calcium carbonate, processing aids such as sodium stearate, calciumstearate, magnesium stearate, barium stearate, liquid paraffin, olefinwax, and a stearyl amide compound, a phenol antioxidant, lightfastnessstabilizers such as a phosphorus-based stabilizer, a nitrogenstabilizer, a sulfur stabilizer, benzotriazoles, and hindered amines,flame retardants other than the substances mentioned above, anantistatic agent, colorants such as a pigment, as necessary, insofar asthe effects of the present invention are not imp aired.

As a procedure of adding various additives to the styrene resin, aprocedure is mentioned, for example, which includes adding variousadditives to the styrene resin and mixing, supplying the mixture to anextruder, heating and melting the mixture, and then further adding afoaming agent. The timing of adding the various additives to the styreneresin and kneading time are not particularly limited.

A method for producing the extruded polystyrene foam of the presentinvention includes supplying styrene resin, a flame retardant, otheradditives, and the like to a heating and melting unit such as anextruder, adding a foaming agent to the styrene resin underhigh-pressure conditions at an arbitrary stage to form a liquid gel,cooling the liquid gel to a temperature suitable for extrusion foaming,and then extrusion foaming the liquid gel to a low-pressure regionthrough a die to form a foam.

The heating temperature may be equal to or higher than the temperatureat which the styrene resin to be used melts and is preferably atemperature at which molecular deterioration of the resin under theinfluence of the additives and the like is suppressed as much aspossible, for example, about 150 to 260° C. The melting and kneadingtime varies depending on the extrusion amount of the styrene resin perunit time and the type of the extruder to be used as the melting andkneading unit and cannot be uniquely specified and is set as appropriateas the time required for uniformly dispersing and mixing the styreneresin and the foaming agent or the additives.

As the melting and kneading unit, a screw type extruder and the like arementioned, for example. However, the melting and kneading unit is notparticularly limited insofar as it is used for usual extrusion foaming.

As a foam molding method of the present invention, a method is used, forexample, which includes molding an extruded foam obtained through a slitdie for use in extrusion molding having an opening of a linear slitshape by opening the same from a high-pressure region to a low-pressureregion into a board-shaped foam having a large cross-sectional areausing a molding the disposed closely contacting or contacting the slitdie, a molding roll disposed adjacent to the downstream side of themolding die, or the like. By adjusting the liquid surface shape of themolding the and adjusting the die temperature, a desired cross-sectionalshape of a foam, desired surface properties of a foam, and a desiredfoam quality are obtained.

The thickness in the extruded polystyrene foam according to the presentinvention is not particularly limited and is preferably 10 mm or moreand 150 mm or less, more preferably 15 mm or more and 120 mm or less,and particularly preferably 20 mm or more and 100 mm or less, forexample, from the viewpoint of heat insulation properties, bendingstrength, and compressive strength considering that the extrudedpolystyrene foam functions as heat insulating materials for constructionor heat insulating materials for cooling boxes or refrigeratingvehicles.

Thus, the present invention can easily provide an extruded polystyrenefoam which is lightweight and has excellent heat insulation propertiesand flame retardancy and has an ozone depletion potential of 0 and a lowglobal warming potential, and thus is friendly to the environment.

EXAMPLES

Hereinafter, Examples of the present invention are described. It is amatter of course that the present invention is not limited to Examplesdescribed below.

Raw materials used in Examples and Comparative Examples are as follows.

Base Material Resin

Styrene resin A [manufactured by PS Japan Corporation, G9401; MFR of 2.2g/10 minutes]

Styrene resin B [manufactured by PS Japan Corporation, 680; MFR of 7.0g/10 minutes]

Flame Retardant

Mixed bromine-based flame retardant of tetrabromobisphenolA-bis(2,3-dibromo-2-methylpropyl)ether and tetrabromobisphenolA-bis(2,3-dibromopropyl)ether [manufactured by Daiichi Kogyo Co., Ltd.,GR-125P]

Brominated styrene-butadiene block polymer [manufactured by ChemturaCorporation, EMERALD INNOVATION #3000]

Hexabromocyclododecane [manufactured by Albemarle Corporation, HP900]

Flame Retardant Assistant

Tris(tribromoneopentyl)phosphate [manufactured by Daihachi ChemicalIndustry Co., Ltd., CR-900]

Triphenylphosphine oxide [Sumitomo Shoji Chemicals Co., Ltd.]

Radical Generating Agent

Poly-1,4-diisopropylbenzene [manufactured by UNITED INITIATORS, CCPIB]

Stabilizer

Bisphenol-A-glycidylether [manufactured by ADEKA Corporation, EP-13]

Cresol novolac type epoxy resin [manufactured by Huntsman Japan KK,ECN-1280]

Dipentaerythritol-adipic acid reaction mixture [manufactured byAjinomoto Fine-Techno Co., Inc., Plenlizer ST210]

Pentaerythritol tetrakis[3-(3′,5′-di-tert-butyl-4′-hydroxyphenynpropionate] [manufactured byChemtura Corporation, ANOX20]

3,9-bis(2,4-di-tert-butylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane[manufactured by Chemtura Corporation, Ultranox626]

Triethyleneglycol bis-3-(3-tert-butyl-4-hydroxy 5-methylphenyl)propionate [manufactured by Songwon Japan, SONGNOX 2450FF]

Other Additives

Calcium stearate [manufactured by Sakai Chemical Industry Co., Ltd.,SC-P]

Bentonite [Hojun., Co. Ltd., Bengel Bright K11]

Silica [manufactured by Evonik Degussa Japan Co., Ltd., Carplex BS-304F]

Foaming Agent

HFO-1234ze [manufactured by Honeywell Japan Inc.]

Diemethyl ether [manufactured by Iwatani Corporation]

Methyl chloride [manufactured by Asahi Glass Co., Ltd.]

Ethyl chloride [manufactured by Nittoku Chemicals]

Isobutane [manufactured by Mitsui Chemicals, Inc.]

Normal butane [manufactured by Iwatani Corporation]

Water [Tap water of Settsu-shi, Osaka-fu]

Examples and Comparative Examples were evaluated for the apparentdensity, the closed cell ratio, the average cell diameter, the celldeformation ratio, the remaining amount of HFO-1234ze based on 100 g ofthe styrene resin in the foam, the thermal conductivity, and the JISflammability according to the following techniques.

(1) Apparent Density (Kg/m³)

The weight of the obtained extruded polystyrene foam was measured andalso the length size, the width size, and the thickness size weremeasured.

The apparent density of the foam was determined from the weight and eachsize measured above according to the following expression, and then theunit was converted to kg/m³.

Apparent density (g/cm³)=Foam weight (g)/Foam volume (cm³)

(2) Closed Cell Ratio (%)

A test piece not having a molded skin of 20 mm in thickness×25 mm inlength×25 mm in width was cut out from the obtained extruded polystyrenefoam and then evaluated according to Procedure C of ASTM-D 2856-70.

(3) Average Cell Diameter (Mm)

The evaluation was performed as described above.

(4) Cell Deformation Ratio

The evaluation was performed as described above.

(5) Remaining Amount of HFO-1234ze Based on 100 g of Styrene Resin inExtruded Foam

The obtained extruded polystyrene foam was allowed to stand still underthe conditions of the standard temperature condition, Third class (23°C.±5° C.) and the standard humidity condition, Third class (50⁺²⁰, ⁻¹⁰%R.H.) specified in JIS K 7100. After the passage of 28 days after theproduction, the remaining amount of HFO-1234ze was evaluated by thefollowing facilities and procedure.

a) Used apparatus; Gas chromatograph GC-2014 [manufactured by ShimadzuCorporation]

b) Used column; G-Column G-950 25UM [manufactured by ChemicalsEvaluation and Research Institute]

c) Measurement conditions;

-   -   Inlet temperature: 65° C.    -   Column temperature: 80° C.    -   Detector temperature: 100° C.    -   Carrier gas: High purity helium    -   Carrier gas flow rate: 30 mL/min.    -   Detector: TCD    -   Current: 120 mA

About 1.2 g of the test piece, which varied depending on the apparentdensity, cut out from the foam, was placed in a glass container(hereinafter referred to as an “airtight container”) capable of sealingabout 130 cc, and then the air in the airtight container was removedusing a vacuum pump. Thereafter, the airtight container was heated at170° C. for 10 minutes, and then the foaming agent in the foam wasextracted in the airtight container. After the temperature of theairtight container returned to normal temperature, helium was introducedinto the airtight container to return the pressure to the atmosphericpressure. Then, 40 μL of the mixed gas containing HFO-1234ze wasextracted by a micro-syringe, and then evaluated with the used apparatusand the measurement conditions of a) to c) above.

(6) Thermal Conductivity (W/mK)

The thermal conductivity of the foam was measured by the methoddescribed above. The criteria for success/failure are as follows.

Success: Thermal conductivity is 0.0280 W/mK or less.

Failure: Thermal conductivity is larger than 0.0280 W/mK.

(7) JIS Flammability

The evaluation was performed using 5 test pieces of 10 mm inthickness×200 mm in length×25 mm in width according to JIS A 9511(Measurement method A) based on the following criteria. The measurementwas performed as follows. After the production of the extrudedpolystyrene foam, the extruded polystyrene foam was cut into test piecesof the dimension mentioned above, and then allowed to stand still underthe conditions of the standard temperature condition, Third class (23°C.±5° C.) and the standard humidity condition, Third class (50⁺²⁰, ⁻¹⁰%R.H.) specified in JIS K 7100. After the passage of 1 week after theproduction, the evaluation was performed.

◯ (Success): Satisfy the standard that flame was extinguished within 3seconds, afterglow did not occur, and burning exceeding the burninglimit indication line did not occur.

x (Failure): Not satisfy the standard.

Example 1 Production of Resin Mixture

Based on 100 parts by weight of the styrene resin A [manufactured by PSJapan Corporation, G9401], 3.0 parts by weight of a mixed bromine-basedflame retardant [manufactured by Daiichi Kogyo Co., Ltd., GR-125P] oftetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether andtetrabromobisphenol A-bis(2,3-dibromopropyl)ether as a flame retardant,1.0 part by weight of a triphenylphosphine oxide [Sumitomo ShojiChemicals Co., Ltd.] as a flame retardant assistant, 0.10 parts byweight of bisphenol A-glycidyl ether [manufactured by ADEKA Corporation,EP-13] and 0.20 parts by weight of triethyleneglycolbis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate [manufactured bySongwon Japan, SONGNOX 2450FF] as a stabilizer, and 0.10 parts by weightof calcium stearate [manufactured by Sakai Chemical Industry Co., Ltd.,SC-P] as a lubricant were dry-blended.

[Production of Extruded Foam]

The obtained resin mixture was supplied at about 50 kg/hr to an extruderin which a single screw extruder (first extruder) with an openingdiameter of 65 mm, a single screw extruder (second extruder) with anopening diameter of 90 mm, and a cooling machine are connected inseries.

The resin mixture supplied to the first extruder was heated to a resintemperature of 240° C. to be melted or plasticized and kneaded, and then4.0 parts by weight (0.035 mol) of HFO-1234ze and 4.7 parts by weight(0.102 mol) of dimethylether as the foaming agent (based on 100 parts byweight of the styrene resin) were pressed into the resin near the tip ofthe first extruder. Thereafter, the resin temperature was reduced to125° C. in the second extruder connected to the first extruder and thecooling machine, and then the resin mixture was extrusion foamed intothe atmosphere at a foaming pressure of 8.0 MPa from a mouthpiece (slitdie) having a rectangular cross section of 1.2 mm in thickness×50 mm inwidth provided at the tip of the cooling machine to give an extrudedfoam board having a cross-sectional shape of 21 mm in thickness×250 mmin width by a molding die disposed closely contacting the mouthpiece anda molding roll disposed on the downstream side thereof.

The evaluation results of the obtained foam are shown in Table 2.

Examples 2 to 12

Foams were obtained by the same operation as that of Example 1 exceptchanging the type and the addition amount of blending ingredients andthe production conditions as shown in Table 2. The physical propertiesof the obtained foams are shown in Table 2.

TABLE 2 Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple5 ple 6 Formula Base resin G9401 parts by weight 100 100 100 100 100 100680 parts by weight 0 0 0 0 0 0 Flame retardant GR-125P parts by weight3.0 3.0 3.0 3.0 3.0 3.0 EMERALD parts by weight 0 0 0 0 0 0 INNOVATION#3000 HBCD (HP900) parts by weight 0 0 0 0 0 0 Stabilizer EP-13 parts byweight 0.10 0.10 0.10 0.10 0.10 0.10 ECN-1280 parts by weight 0 0 0 0 00 Plenlizer ST210 parts by weight 0 0 0 0 0 0 ANOX20 parts by weight 0 00 0 0 0 Utranox626 parts by weight 0 0 0 0 0 0 SONGNOX 2450FF parts byweight 0.20 0.20 0.20 0.20 0.20 0.20 Flame retardant Triphenylphos-parts by weight 1.0 1.0 1.0 1.0 1.0 1.0 assistant phine oxide CCPIBparts by weight 0 0 0 0 0 0 CR-900 parts by weight 0 0 0 0 0 0 Foamingagent HFO-1234ze parts by weight 4.0 6.0 8.0 8.0 8.0 8.0 Isobutane partsby weight 0 0 0 0 0 0 Normal butane parts by weight 0 0 0 0 0 0 Dimethylether parts by weight 4.7 4.0 3.2 2.7 5.0 0 Methyl chloride parts byweight 0 0 0 0 0 3.5 Ethyl chloride parts by weight 0 0 0 0 0 0 Waterparts by weight 0 0 0 0 0 0 Blended amount HFO-1234ze mol 0.035 0.0530.070 0.070 0.070 0.070 of foaming agent Isobutane mol 0 0 0 0 0 0(Based on 100 g Normal butane mol 0 0 0 0 0 0 of styrene resin) Dimethylether mol 0.102 0.087 0.069 0.059 0.109 0 Methyl chloride mol 0 0 0 0 00.069 Ethyl chloride mol 0 0 0 0 0 0 Total mol 0.137 0.139 0.140 0.1290.179 0.139 Lubricant SC-P parts by weight 0.10 0.10 0.10 0.10 0.10 0.10Water absorbing Bengel Bright K11 parts by weight 0 0 0 0 0 0 mediumCarplex BS-304F parts by weight 0 0 0 0 0 0 Production Foamingtemperature ° C. 125 124 126 125 125 126 conditions Die pressure MPa 8.08.2 8.0 7.9 8.1 8.0 Physical Apparent density kg/m³ 35 35 35 35 35 35properties Closed cell ratio % 95 96 96 95 95 96 of extruded Averagecell diameter mm 0.1 0.1 0.1 0.1 0.1 0.1 foam Cell deformation ratio —1.0 1.0 1.0 1.0 1.0 1.0 Remaining amount of HFO-1234ze based on mol0.032 0.050 0.068 0.068 0.068 0.068 100 g of styrene resin in extrudedfoam (After passage of 28 days after production) Thermal conductivityW/mK 0.0277 0.0272 0.0267 0.0266 0.0268 0.0268 (After passage of 100days after production) JIS flammability — ∘ ∘ ∘ ∘ ∘ ∘ Exam- Exam- Exam-Exam- Exam- Exam- ple 7 ple 8 ple 9 ple 10 ple 11 ple 12 Formula Baseresin G9401 parts by weight 100 100 100 100 0 100 680 parts by weight 00 0 0 100 0 Flame retardant GR-125P parts by weight 3.0 3.0 1.0 5.0 0 0EMERALD parts by weight 0 0 0 0 3.0 0 INNOVATION #3000 HBCD (HP900)parts by weight 0 0 0 0 0 3.0 Stabilizer EP-13 parts by weight 0.10 0.100.10 0.10 0.15 0.10 ECN-1280 parts by weight 0 0 0 0 0.15 0 PlenlizerST210 parts by weight 0 0 0 0 0.20 0 ANOX20 parts by weight 0 0 0 0 0.300 Utranox626 parts by weight 0 0 0 0 0.015 0 SONGNOX 2450FF parts byweight 0.20 0.20 0.20 0.20 0 0.20 Flame retardant Triphenylphos- partsby weight 1.0 1.0 1.0 1.0 0.50 0 assistant phine oxide CCPIB parts byweight 0 0 0 0 0.10 0 CR-900 parts by weight 0 0 0 0 0 1.0 Foaming agentHFO-1234ze parts by weight 8.0 8.0 8.0 8.0 8.0 8.0 Isobutane parts byweight 0 0 0 0 0 0 Normal butane parts by weight 0 0 0 0 0 0 Dimethylether parts by weight 0 3.3 3.2 3.2 3.2 3.2 Methyl chloride parts byweight 0 0 0 0 0 0 Ethyl chloride parts by weight 4.6 0 0 0 0 0 Waterparts by weight 0 0.7 0 0 0 0 Blended amount HFO-1234ze mol 0.070 0.0700.070 0.070 0.070 0.070 of foaming agent Isobutane mol 0 0 0 0 0 0(Based on 100 g Normal butane mol 0 0 0 0 0 0 of styrene resin) Dimethylether mol 0 0.072 0.069 0.069 0.069 0.069 Methyl chloride mol 0 0 0 0 00 Ethyl chloride mol 0.071 0 0 0 0 0 Total mol 0.141 0.142 0.140 0.1400.140 0.140 Lubricant SC-P parts by weight 0.10 0.10 0.10 0.10 0.10 0.10Water absorbing Bengel Bright K11 parts by weight 0 0.40 0 0 0 0 mediumCarplex BS-304F parts by weight 0 0.40 0 0 0 0 Production Foamingtemperature ° C. 124 122 125 126 120 125 conditions Die pressure MPa 8.08.0 8.1 8.1 8.0 7.9 Physical Apparent density kg/m³ 35 35 35 35 35 35properties Closed cell ratio % 95 95 97 95 96 95 of extruded Averagecell diameter mm 0.1 0.1 0.1 0.1 0.1 0.1 foam Cell deformation ratio —1.0 1.0 1.0 1.0 1.0 1.0 Remaining amount of HFO-1234ze based on mol0.068 0.068 0.068 0.068 0.068 0.068 100 g of styrene resin in extrudedfoam (After passage of 28 days after production) Thermal conductivityW/mK 0.0265 0.0268 0.0266 0.0266 0.0268 0.0269 (After passage of 100days after production) JIS flammability — ∘ ∘ ∘ ∘ ∘ ∘

Comparative Examples 1 to 7

Foams were obtained by the same operation as that of Example 1 exceptchanging the type and the addition amount of blending ingredients andthe production conditions as shown in Table 3. The physical propertiesof the obtained foam are shown in Table 3.

TABLE 3 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Formula Base resin G9401 parts by weight100 100 100 100 680 parts by weight 0 0 0 0 Flame retardant GR-125Pparts by weight 3.0 3.0 3.0 3.0 EMERALD parts by weight 0 0 0 0INNOVATION #3000 HBCD (HP900) parts by weight 0 0 0 0 Stabilizer EP-13parts by weight 0.10 0.10 0.10 0.10 ECN-1280 parts by weight 0 0 0 0Plenlizer ST210 parts by weight 0 0 0 0 ANOX20 parts by weight 0 0 0 0Ultranox626 parts by weight 0 0 0 0 SONGNOX 2450FF parts by weight 0.200.20 0.20 0.20 Flame retardant Triphenylphos- parts by weight 1.0 1.01.0 1.0 assistant phine oxide CCPIB parts by weight 0 0 0 0 CR-900 partsby weight 0 0 0 0 Foaming agent HFO-1234ze parts by weight 8.0 8.0 2.615.0 Isobutane parts by weight 4.1 0 0 0 Normal butane parts by weight 04.1 0 0 Dimethyl ether parts by weight 0 0 5.2 0.6 Methyl chloride partsby weight 0 0 0 0 Ethyl chloride parts by weight 0 0 0 0 Water parts byweight 0 0 0 0 Blended amount HFO-1234ze mol 0.070 0.070 0.023 0.132 offoaming agent Isobutane mol 0.071 0 0 0 (Based on 100 g Normal butanemol 0 0.071 0 0 of styrene resin) Dimethyl ether mol 0 0 0.113 0.013Methyl chloride mol 0 0 0 0 Ethyl chloride mol 0 0 0 0 Total mol 0.1410.141 0.136 0.145 Lubricant SC-P parts by weight 0.10 0.10 0.10 0.10Water absorbing Bengel Bright K11 parts by weight 0 0 0 0 medium CarplexBS-304F parts by weight 0 0 0 0 Production Foaming temperature ° C. 125126 126 125 conditions Die pressure MPa 8.0 8.1 8.0 8.0 PhysicalApparent density kg/m³ 35 35 35 Generation of a properties Closed cellratio % 96 95 99 large amount of of extruded Average cell diameter mm0.1 0.1 0.1 spot holes foam Cell deformation ratio — 1.0 1.0 1.0Uncollectable Remaining amount of HFO-1234ze based on mol 0.068 0.0680.020 due to poor 100 g of styrene resin in extruded foam molding (Afterpassage of 28 days after production) Thermal conductivity W/mK 0.02710.0269 0.0283 (After passage of 100 days after production) JISflammability — x x ∘ Comparative Comparative Comparative Example 5Example 6 Example 7 Formula Base resin G9401 parts by weight 100 100 100680 parts by weight 0 0 0 Flame retardant GR-125P parts by weight 3.03.0 8.0 EMERALD parts by weight 0 0 0 INNOVATION #3000 HBCD (HP900)parts by weight 0 0 0 Stabilizer EP-13 parts by weight 0.10 0.10 0.10ECN-1280 parts by weight 0 0 0 Plenlizer ST210 parts by weight 0 0 0.10ANOX20 parts by weight 0 0 0 Ultranox626 parts by weight 0 0 0 SONGNOX2450FF parts by weight 0.20 0.20 0.20 Flame retardant Triphenylphos-parts by weight 1.0 1.0 1.0 assistant phine oxide CCPIB parts by weight0 0 0 CR-900 parts by weight 0 0 0 Foaming agent HFO-1234ze parts byweight 8.0 8.0 8.0 Isobutane parts by weight 0 0 0 Normal butane partsby weight 0 0 0 Dimethyl ether parts by weight 0 1.5 3.2 Methyl chlorideparts by weight 0 0 0 Ethyl chloride parts by weight 0 0 0 Water partsby weight 0 0 0 Blended amount HFO-1234ze mol 0.070 0.070 0.070 offoaming agent Isobutane mol 0 0 0 (Based on 100 g Normal butane mol 0 00 of styrene resin) Dimethyl ether mol 0 0.033 0.069 Methyl chloride mol0 0 0 Ethyl chloride mol 0 0 0 Total mol 0.070 0.103 0.140 LubricantSC-P parts by weight 0.10 0.10 0.10 Water absorbing Bengel Bright K11parts by weight 0 0 0 medium Carplex BS-304F parts by weight 0 0 0Production Foaming temperature ° C. 126 126 125 conditions Die pressureMPa 8.0 7.9 7.9 Physical Apparent density kg/m³ 51 43 Uncollectableproperties Closed cell ratio % 76 82 due to poor of extruded Averagecell diameter mm 0.1 0.1 molding foam Cell deformation ratio — 1.0 1.0Remaining amount of HFO-1234ze based on mol 0.068 0.068 100 g of styreneresin in extruded foam (After passage of 28 days after production)Thermal conductivity W/mK 0.0304 0.0296 (After passage of 100 days afterproduction) JIS flammability — ∘ ∘

As is clear from the comparison between Examples 1 to 12 shown in Table2 and Comparative Examples 1 to 7 shown in Table 3, by extrusion foammolding of a styrene resin containing predetermined amounts of a flameretardant and a mixed foaming agent in accordance with the presentinvention, an extruded polystyrene foam which is lightweight and hasexcellent heat insulation properties and flame retardancy and has anozone depletion potential of 0 and a low global warming potential, andthus is friendly to the environment can be obtained.

1. An extruded polystyrene foam, comprising: a styrene resin; and from0.5 parts by weight to 8.0 parts by weight of a flame retardant based on100 parts by weight of the styrene resin, wherein the extrudedpolystyrene foam is obtained by the process comprising extruding astyrene resin composition comprising the styrene resin, the flameretardant, and a foaming agent, wherein the extruded polystyrene foamhas an apparent density of from 20 kg/m³ to 45 kg/m³ and a closed cellratio of 90% or more, the foaming agent comprises hydrofluoroolefin anda second organic foaming agent, an amount of the hydrofluoroolefin isfrom 0.030 mol to 0.125 mol based on 100 g of the styrene resin, thesecond organic foaming agent comprises an organic foaming agent having apolystyrene permeability of 0.5×10⁻¹⁰ cc·cm/cm²·s·cmHg or more and doesnot comprise an organic foaming agent having a polystyrene permeabilityof less than 0.5×10⁻¹⁰ cc·cm/cm²·s·cmHg, and a total amount of thehydrofluoroolefin and the second organic foaming agent is from 0.105 molto 0.300 mol based on 100 g of the styrene resin.
 2. The extrudedpolystyrene foam according to claim 1, wherein the amount of thehydrofluoroolefin is from 0.040 mol to 0.105 mol based on 100 g of thestyrene resin.
 3. The extruded polystyrene foam according to claim 1,wherein the hydrofluoroolefin is tetrafluoropropene.
 4. The extrudedpolystyrene foam according to claim 1, wherein the second organicfoaming agent is at least one organic foaming agent selected from thegroup consisting of dimethylether, methyl chloride, and ethyl chloride.5. The extruded polystyrene foam according to claim 1, wherein thesecond organic foaming agent is dimethylether.
 6. The extrudedpolystyrene foam according to claim 1, wherein the flame retardantcomprises from 0.5 parts by weight to 6.0 parts by weight of abromine-based flame retardant based on 100 parts by weight of thestyrene resin.
 7. A method for producing an extruded polystyrene foam,the method comprising: heating and melting a styrene resin compositioncomprising a styrene resin and from 0.5 parts by weight to 8.0 parts byweight of a flame retardant based on 100 parts by weight of the styreneresin; adding a foaming agent to the heated and melted styrene resincomposition under a high-pressure condition such that a mixture isprepared; cooling the mixture to a predetermined resin temperature; andthen extruding the cooled mixture into a low-pressure area such that anextruded foam is formed, wherein the extruded foam has an apparentdensity of from 20 kg/m³ to 45 kg/m³ and a closed cell ratio of 90% ormore, the foaming agent comprises hydrofluoroolefin and a second organicfoaming agent, an amount of the hydrofluoroolefin is from 0.030 mol to0.125 mol based on 100 g of the styrene resin, the second organicfoaming agent comprises an organic foaming agent having a polystyrenepermeability of 0.5×10⁻¹° cc·cm/cm²·s·cmHg or more and does not comprisean organic foaming agent having a polystyrene permeability of less than0.5×10⁻¹° cc·cm/cm²·s·cmHg, and a total amount of the hydrofluoroolefinand the second organic foaming agent is from 0.105 mol to 0.300 molbased on 100 g of the styrene resin.
 8. The extruded polystyrene foamaccording to claim 1, wherein the styrene resin comprises a polystyreneresin.
 9. The extruded polystyrene foam according to claim 1, whereinthe hydrofluoroolefin is tetrafluoropropene, and the second organicfoaming agent is at least one organic foaming agent selected from thegroup consisting of dimethylether, methyl chloride, and ethyl chloride.10. The extruded polystyrene foam according to claim 2, wherein thehydrofluoroolefin is tetrafluoropropene, and the second organic foamingagent is at least one organic foaming agent selected from the groupconsisting of dimethylether, methyl chloride, and ethyl chloride. 11.The extruded polystyrene foam according to claim 1, wherein thehydrofluoroolefin is tetrafluoropropene, and the second organic foamingagent is dimethylether.
 12. The extruded polystyrene foam according toclaim 2, wherein the hydrofluoroolefin is tetrafluoropropene, and thesecond organic foaming agent is dimethylether.
 13. The extrudedpolystyrene foam according to claim 1, wherein the amount of thehydrofluoroolefin is from 0.045 mol to 0.090 mol based on 100 g of thestyrene resin.
 14. The extruded polystyrene foam according to claim 1,wherein the total amount of the hydrofluoroolefin and the second organicfoaming agent is from 0.115 mol to 0.200 mol based on 100 g of thestyrene resin.
 15. The extruded polystyrene foam according to claim 1,wherein the foaming agent further comprises an inorganic foaming agent.16. The extruded polystyrene foam according to claim 2, wherein theamount of the hydrofluoroolefin is from 0.040 mol to 0.105 mol based on100 g of the styrene resin.